The present invention relates to automatic packaging machines, in particular for wrapping articles with heat-sealing material.
Different types of articles are packaged with flexible synthetic material, which can be heat-welded.
From now on, reference will be made to packaging of paper rolls, e.g. tissue paper towels, which are wrapped within a sheet of heat-sealing material, e.g. polythene.
The rolls are moved, e.g. in pairs, toward a packaging station and during the run, they strike against the sheet of polythene and pull it with them, thus wrapping themselves with it.
Additional means fold the edges of the sheet under the rolls, which are kept in position by prongs of a conveyor situated and working over the packaging station.
The packaged articles are moved by the pronged conveyor, and during the movement on a running surface adjacent to the packaging station, the wrapping is heat-sealed along the overlapped edges.
The heads of the package, from which ring-like edges protrude, are still open and they are closed by heat-sealing in a subsequent station of the machine.
FIG. 1 shows the station of the machine, in which the heads of the packages are closed, with particular attention to the passage section from the pronged conveyor, indicated with 1, to a conveyor 2 with vertical sealing belts 3, situated downstream.
The packages 5 move forward on the running surface 12 of the prong conveyor 1. The packages 5 are kept between the pairs of adjacent prongs 13 and their upper part is stabilized by a series of motionless stops 6, including e.g. one or more bars, extending longitudinally with respect to the conveyor.
Actually, each of the prongs 13 as shown includes two or more prongs, which are aligned crosswise to the conveyor.
After having reached the terminal area ZT of the prong conveyor 1, the packages 5 are picked up from the vertical belts 3 of the belt conveyor 2 in the inlet area ZI thereof.
In the terminal area ZT, the prong conveyor 1 follows a circular trajectory, inverting the movement direction, so as to close in an endless loop in the upper run of its extension. As shown in FIG. 1, the free ends of the prongs 13, which pull the packages 5, tend to push the latter and to raise them in the area where the conveyor rotates, due to the acceleration imposed to the packages by the circular trajectory.
This movement of the package tends to set the wrapping into disorder and, in any case, it is undesirable for the package, whose appearance is no longer the best.
In order to avoid this problem, the vertical sealing belts 3 are usually operated to move much faster than the prong conveyor 1, so that the packages 5 are accelerated in the terminal area ZT and is no longer subjected to the action of the prongs 13 when the latter begins to curve upwards.
The sealing belts 3 are made of a material which can be heated and then, after having heated the overlapped edges of the packages 5 heads, it softens the heated edges and makes them adhere to each other, thus closing definitely the package. However, this kind of material does not react well to the stresses which the belts are subjected to in the curved areas of the return points.
The consequent damages are even bigger because of higher speed, with which the sealing belts are operated. This results in the necessity of frequent substitutions of the sealing belts, which increases considerably the costs.
Moreover, the higher speed of the sealing belts causes higher sealing temperature, since the sealing time is reduced. This provokes a bigger waste of energy.
The object of the present invention is to change the constructive characteristics of the device, so as to avoid the problem of stress, to which the packages are subjected due to the circular trajectory of the prongs, without operating the sealing belts with a speed higher than the minimum speed required by the packaging line operation, thus prolonging considerably the duration of the sealing belts.
Another object of the present invention is to obtain what above by a simple, functional and cheap solution, which does not affect remarkably the total cost of the equipment, nor of its subsequent maintenance.
The above mentioned objects are obtained, in accordance with the contents of the claims, by means of a device for accelerated conveying of packages in between two vertical belts at an inlet area, said package being brought by a conveyor including:
a running surface for the packages;
a terminal area of said running surface situated at a distance from said inlet area of said vertical belts;
series of stationary stops disposed above the running surface to constrain said packages;
a plurality of vertical prongs extending underneath said stops and above said running surface for moving the packages, said vertical prongs moving along a path which follows a circular trajectory at the terminal area;
said device including a forwarding belt, coplanar with said running surface of said conveyor, situated between said inlet area of said vertical belts and said terminal area of said conveyor, said forwarding belt being operated with a speed higher than the operation speed of said conveyor.